1. Field of the Invention
The present invention relates to a method of preparing a toner and a toner prepared using the method. More particularly, the present invention relates to a method of preparing a toner by forming a core using a latex particle and a shell layer by coating the core, a toner prepared using the method, an image forming method using the toner, and an image forming apparatus employing the toner.
2. Description of the Related Art
In an electrophotographic process or an electrostatic recording process, a developer used to form an electrostatic image or an electrostatic latent image may be a two-component developer formed of a toner and carrier particles, or a one-component developer formed of a toner only. The one-component developer may be a magnetic one-component developer having magnetic properties or a nonmagnetic one-component developer having no magnetic properties. Plasticizers such as colloidal silica are often added independently to the nonmagnetic one-component developer to increase the flowability of the toner. Generally, coloring particles obtained by dispersing a colorant, such as carbon black or other additives in a binding resin, are used in the toner.
Methods of preparing toners include pulverization or polymerization. In pulverization, the toner is obtained by melt mixing synthetic resins with colorants and, if needed, other additives. The mixture is then pulverized and particles are sorted until particles of a desired size are obtained. In polymerization, a polymerizable monomer composition is manufactured by uniformly dissolving or dispersing a polymerizable monomer, a colorant, a polymerization initiator and, if needed, various additives such as a cross-linking agent and an antistatic agent. Next, the polymerizable monomer composition is dispersed in an aqueous dispersive medium which includes a dispersion stabilizer using an agitator to form minute liquid droplet particles. Subsequently, the temperature is increased and suspension polymerization is performed to obtain a polymerized toner having color polymer particles of a desired size.
In an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an electrostatic latent image is formed through light-exposing the surface of a photoreceptor that is uniformly charged. A toner is attached to the electrostatic latent image, and a resulting toner image is transferred to a transfer medium such as a paper through several processes such as heating, pressing, solvent steaming, or the like. In most fixing processes, the transfer medium with the toner image passes through fixing rollers and pressing rollers, and by heating and pressing, the toner image is fused to the transfer medium.
Images formed by an image forming apparatus such as an electrophotocopier should satisfy requirements of high precision and accuracy. Conventionally, a toner used in an image forming apparatus is usually obtained using pulverization. When using pulverization, coloring particles having a wide range of sizes are likely formed. Hence, to obtain satisfactory developer properties, there is a need to sort the color particles obtained through pulverization according to size in order to reduce the particle size distribution. However, it is difficult to precisely control the particle size distribution using a conventional mixing/pulverizing process in the manufacture of toner particles suitable for an electrophotographic process or electrostatic recording process. Also, when preparing a minute particle toner, a toner preparation yield is low due to a sorting process. In addition, there is a limit to a change/adjustment of a toner design for obtaining desirable charging and fixing properties. Accordingly, polymerized toners, in which the size of particles is easy to control and which do not need to undergo a complex manufacturing process such as sorting, have come into spotlight recently.
When a toner is prepared using polymerization, a desired size distribution of particles is obtained without performing pulverization or sorting.
U.S. Pat. No. 6,033,822 to Hasegawa et al. discloses a polymerized toner including a core formed of colored polymer particles and a shell covering the core in molecules, wherein the polymerized toner is prepared by suspension polymerization, the entire disclosure of which is hereby incorporated by reference. However, it is still difficult to adjust the shape of the toner and the sizes of the particles. Also, the there is a wide distribution of particle sizes.
U.S. Pat. No. 6,258,911 to Michael et al. discloses a bi-functional polymer having a narrow polydispersity and an emulsion-condensation polymerization process for manufacturing a polymer having covalently bonded free radicals on each end, the entire disclosure of which is hereby incorporated by reference. However, even when this method is used, a surfactant can cause an adverse effect, and it is difficult to control the size of latex.
Accordingly, there is a need for an improved toner and method of preparing a toner having superior properties in particle size control, storability, durability, or the like.